The present invention relates to an apparatus for detecting misfires of an internal combustion engine and a method for detecting the misfires of the internal combustion engine.
One example of a misfire detecting apparatus for an internal combustion engine is shown in Japanese Patent Publication No. 2905937. This apparatus is explained using FIG. 8.
With reference to FIG. 8, a block diagram consists of a circuit of determining sphere 51, a circuit of memorizing a basic value 52, a circuit of calculating a rate of misfire 53, a comparing circuit 54, a driving circuit 55, and a warning means 56. The circuit of determining sphere 51 determines to which sphere a condition of an internal combustion engine belongs by revolutions of the engine and an intake air amount of the engine. The circuit of memorizing a basic value 52 memorizes a basic rate of misfire for which a predetermined value is set in each driving condition sphere. The circuit of calculating a rate of misfire 53 detects misfires of the internal combustion engine by a fluctuation of combustion pressure of the engine at a predetermined crank angle in a predetermined driving sphere of the internal combustion engine, and it calculates the rate of misfire by a number of misfires per a constant number of ignitions of the engine. The comparing circuit 54 compares the actual rate of misfire outputted at the circuit of calculating rate of misfire 53 with the basic rate of misfire outputted at the circuit of memorizing a basic value 52. Furthermore, the comparing circuit 54 determines that the engine is out of order if the detected actual rate of misfire is greater than the basic rate of misfire, and the comparing circuit 54 sends a driving signal indicating that the engine has a problem to the driving circuit 55. The warning means 56 gives an alarm by the signal from the driving circuit 55.
As mentioned above, it is necessary that the basic rate of misfire is low in this misfire detecting apparatus, because an ability of cleansing an exhaust gas of a catalytic converter is low at cold start condition of the internal combustion engine. When the basic rate of misfire remains low, a possibility that the engine is misjudged as a trouble is high, though the misfire is caused by fuel properties (ex. containing alcohol), not by the engine trouble, at hot start condition under which the high basic rate of misfire is allowable because the ability of cleansing by the catalytic converter is high.
It is thus one object of the present invention to solve the aforementioned problems. That is, the object of the invention is to provide a misfire detecting apparatus for an internal combustion engine which detects a misfire of an internal combustion engine. Another object of the invention is to provide a method of detecting the misfire of the internal combustion engine.
An apparatus for detecting a misfire of an internal combustion engine comprises a start determinator, a rotation counter, a misfire detector, a misfire calculator, a setting means, an abnormality determinator, and a warning means. The start determinator determines a starting condition of the internal combustion engine. The rotation counter counts a total number of rotations of the internal combustion engine. The misfire detector detects a misfire of the internal combustion engine. The misfire calculator calculates a rate of misfire using data from the misfire detector, and the rate of misfire is the number of misfires per a predetermined total number of rotations. The setting means sets a basic rate of misfire in response to the start condition of the internal combustion engine. The abnormality determinator determines an abnormal condition of the internal combustion engine when the rate of misfire calculated by the misfire calculator is greater than the basic rate of misfire set by the setting means. The warning means warns of an abnormality of the internal combustion engine when the abnormality determinator determines abnormal condition of the internal combustion engine.
Since the abnormal condition of the internal combustion engine is determined by comparing the actual rate of misfire with the basic rate of misfire, and since the basic rate of misfire is varied in response to the start condition of the internal combustion engine, a possibility that an incorrect detection whether the engine is abnormal or not could happen can be low. Then, the detection accuracy can be secured.